The present invention relates to a sheathed optical fiber cutting method and apparatus.
There are sheathed optical fibers that are drawn from an optical fiber mother material and have a sheath on an optical fiber (bare fiber bearing no coat on its outer surface) made of a core and a clad. It is necessary to cut such a sheathed optical fiber as follows in one step in order to efficiently and accurately measure the decentering of the sheath and mode fields such as the refractive index distribution. Namely, a sheathed optical fiber needs cutting so that no step is left between the sheath and the optical fiber as well as its sheared edge is perpendicular to the axial direction.
The prior art cutting apparatus for sheathed optical fibers meeting the above needs holds the sheathed optical fiber 1 having an optical fiber 1a and a sheath 1b with right and left clamps 2 and 3, as shown in FIG. 15, for example. A cutting blade 4 that slides between the clamps 2 and 3 is pushed onto the sheathed optical fiber 1 to make an incision in the fiber. Afterward, a block 5 facing the cutting blade 4 pushes the sheathed optical fiber 1 to cut the sheathed optical fiber 1.
In this type of cutting apparatuses, the cutting blade 4 may cut the sheathed optical fiber 1, with the sheathed optical fiber 1 being held by the right and left clamps 2 and 3 and provided with tension in its longitudinal direction. In other cases, after the right and left clamps 2 and 3 have clamped the sheathed optical fiber 1, either clamp moves away from the other, and then the sheathed optical fiber 1 is cut, being provided with tension.
Meanwhile, there are proposed cutting apparatuses like those shown in FIGS. 16A and 16B that can cut a sheathed optical fiber without leaving a step between its sheath and optical fiber to provide a flat sheared edge perpendicular to the axial direction.
Such cutting apparatuses hold the sheath 1b at the end of the sheathed optical fiber 1 with the clamp 3 and the optical fiber 1a from which the sheath 1b has been removed with the clamp 2, respectively. The optical fiber 1a is cut by the cutting blade 4 between the clamps 2 and 3. The clamp 3 fixing the sheath 1b has an elastic body 6 such as a spring that repels to the opposite direction to the cutting blade 4 to provide the sheathed optical fiber 1 with constant tension.
These cutting apparatuses further have, between the clamp 3 and the cutting blade 4, tension providing means 9 having a slope 7 and an index plunger 8. The slope 7 is formed on the clamp 3 so that it gradually increases the tension applied to the sheathed optical fiber 1 after an incision is made on the sheathed optical fiber 1 by sliding the cutting blade 4 until the sheathed optical fiber is cut. The index plunger 8 is mounted on the side of the cutting blade 4 and its end is pushed against the slope 7.
However, in the cutting apparatus shown in FIG. 15, a compressive stress is applied to the sheath because the edge of the cutting blade 4 digs into the incision made in the sheath of the sheathed optical fiber 1 during the cutting of the sheathed optical fiber 1. As a result, the sheath is likely to collapse when employing this type of cutting apparatuses, and the edge of the cutting blade 4 often slips off the sheath because of the elasticity of the sheath. Besides, because the cutting blade 4 digs into the sheathed optical fiber 1 from a single direction, the sheath is torn during cut and the cutting of the optical fiber inside the sheath is affected.
Therefore, using the cutting apparatus shown in FIG. 15, it is difficult to cut the sheathed optical fiber 1, leaving no step between the sheath and the optical fiber, and to provide a flat sheared edge perpendicular to the axial direction.
Meanwhile, the cutting apparatuses shown in FIGS. 16A and 16B remove the sheath 1b of the sheathed optical fiber 1 and then cut only the optical fiber 1a. Those cutting apparatuses thus need a preliminary process for removing the sheath 1b prior to cutting, requiring two steps for cutting the sheathed optical fiber 1.
An object of the present invention is to provide a sheathed optical fiber cutting method and apparatus that can cut sheathed optical fibers, leaving no step between the sheath and the optical fiber, and provide a flat sheared edge perpendicular to the axial direction in a single step.
In order to solve the above problems, a sheathed optical fiber cutting method based on a first aspect of the present invention is constituted in such a manner that an incision is made by a cutting blade, under such a condition that the sheathed optical fiber is relatively rotated around its center axis against the cutting blade and bent, in an area having a bent curvature larger than that of the center of the bent optical fiber along the center axis, from the tension-applied surface to which a tension is applied due to fiber bending toward the fiber center, and the sheathed optical fiber is cut.
In the sheathed optical fiber cutting method based on the first aspect, the sheathed optical fiber cutting method based on a second aspect of the present invention is constituted in such a manner that the sheath of the sheathed optical fiber is sheared and then the optical fiber where a cutout has been made is cut.
Further in the sheathed optical fiber cutting method based on the first aspect, the sheathed optical fiber cutting method based on a third aspect of the present invention is constituted in such a manner that the cutting blade makes the incision in the tension-applied surface under such a condition that the sheathed optical fiber is pulled along its axial direction.
A sheathed optical fiber cutting apparatus based on a fourth aspect of the present invention comprises: a clamp part that holds the sheathed optical fiber; a cutting blade that makes an incision toward the center of the sheathed optical fiber; a blade block that is located against the cutting blade beyond the sheathed optical fiber and supports the sheathed optical fiber where an incision is to be made by the cutting blade; tension providing means for forming in the sheathed optical fiber a tension-applied surface to which a tension due to fiber bending is applied by pushing and bending the blade block onto the sheathed optical fiber and having a mechanism of relatively pushing the tension-applied surface onto the cutting blade; and rotating means for relatively rotating the sheathed optical fiber around its center axis against the cutting blade.
The sheathed optical fiber cutting apparatus based on a fifth aspect of the invention is the sheathed optical fiber cutting apparatus based on the fourth aspect of the invention, wherein the tension providing means further has a tension providing mechanism for providing additional tension to the tension-applied surface of the sheathed optical fiber by pulling the sheathed optical fiber to its axial direction in order to gradually increase the tension applied to the sheathed optical fiber as the incision made by the cutting blade becomes deeper.
The sheathed optical fiber cutting apparatus based on a sixth aspect of the invention is the sheathed optical fiber cutting apparatus based on the fourth or fifth aspect of the invention, wherein the cutting blade is mounted in vibration generating means for vibrating in a radial direction of the sheathed optical fiber.
The sheathed optical fiber cutting apparatus based on a seventh aspect of the invention is the sheathed optical fiber cutting apparatus based on the fourth, fifth or sixth aspect of the invention, wherein; the cutting blade comprises a first cutting blade for cutting the sheath of the sheathed optical fiber and a second cutting blade for cutting the optical fiber, and the first and second cutting blades are mounted in a cutting blade exchange guide so that they may shuttle between an operation position for cutting the sheath of the sheathed optical fiber or the optical fiber and a position for standby.
According to the sheathed optical fiber cutting methods and cutting apparatus based on the first, second and fourth aspects of the present invention, a cutting blade makes an incision in an area having a bent curvature larger than that of the center line of the bent fiber along the optical axis, from a tension-applied surface to which a tension is applied by the bending of the sheathed optical fiber toward the fiber center, holding the sheathed optical fiber in a curved state. Then the incision created in the sheathed optical fiber broadens from the fiber center side toward the outside radial direction to the tension-applied surface, seen from the transverse direction perpendicular to the optical axis. Therefore, the contact friction between the cutting blade and the incision in the sheathed optical fiber as well as the compression stress exerted on the sheath of the sheathed optical fiber and the optical fiber become small. As a result, the sheath of the sheathed optical fiber near the incision does not collapse, or the sheared edge of the sheath or the optical fiber does not become rough. Furthermore, the edge of the cutting blade does not slip away from the sheath because of the elasticity of the sheath of the sheathed optical fiber.
Further, according to the sheathed optical fiber cutting method of the present invention, the cutting blade makes an incision in the tension-applied surface of the sheathed optical fiber by relatively rotating the sheathed optical fiber around its center axis against the cutting blade. Therefore, the incision develops uniformly in the outer surface in the circumferential direction, eliminating the problem that when cutting a sheathed optical fiber the sheath is torn off and the sheared edge becomes uneven (rough).
Thus it is possible to cut the sheathed optical fiber so that the sheared edge is flat and perpendicular to the axial direction in a single step, leaving no step between the sheath and the optical fiber. It also becomes possible to accurately measure the decentering of the sheath of the sheathed optical fiber and the mode fields such as the refractive index distribution efficiently and accurately in a single step.
Further, the sheath of the sheathed optical fiber is sheared at an incision made by the cutting blade and then the optical fiber is sheared after a cutout has been made. Therefore, the sheared edge of the sheath becomes flat and the fracture edge of the optical fiber becomes mirror-flat. Therefore, it becomes possible to easily and quickly perform after-treatment like edge polishing; it may be possible to skip after-treatment.
According to the sheathed optical fiber cutting method and cutting apparatus based on the third and fifth aspects of the present invention, the sheathed optical fiber is relatively rotated around its center axis against a cutting blade, curved and pulled along its axial direction at the same time. In this state, the cutting blade makes an incision in an area having a bent curvature larger than that of the center of the bent fiber along the center axis, from the tension-applied surface to the fiber center, to cut the optical fiber. Thus the sheathed optical fiber does not require bending strongly with a small curvature. In other words, it is possible to form an outer surface to which a tension is applied due to fiber bending by gently curving the sheathed optical fiber with a large radius of curvature. When the sheathed optical fiber is bent, while being relatively rotated around its center axis against the cutting blade, no excessive torsion is applied to the sheathed optical fiber and thus there is no damage caused to the optical fiber. At the same time, since it becomes easy to relatively rotate and bend the optical fiber, the structure of the cutting apparatus becomes simple.
If the cutting blade makes an incision in the tension-applied surface under such a condition that the sheathed optical fiber is relatively rotated and bent as well as pulled in the axial direction at the same time, the tension applied to the optical fiber gradually increases as the incision made by the cutting blade develops deep. As a result, since the incision in the sheathed optical fiber made by the cutting blade easily widens, the contact friction between the cutting blade and the incision becomes smaller. So, it is preferable that, it becomes possible to make the sheared edges, made by the cutting blade, of the sheath and the optical fiber of the sheathed optical fiber easily flat.
According to the sheathed optical fiber cutting apparatus based on the sixth aspect of the present invention, the cutting blade is mounted on the vibration generating means that vibrates in the radial direction of the sheathed optical fiber. In such a cutting apparatus, since the friction exerted on the contact face between the cutting blade and the sheathed optical fiber becomes smaller when cutting the sheathed optical fiber through making an incision with the cutting blade, it is ensured to provide a flatter sheared edge.
According to the sheathed optical fiber cutting apparatus based on the seventh aspect of the present invention, a first cutting blade for cutting the sheath of the sheathed optical fiber and a second cutting blade for cutting the optical fiber are prepared as cutting blades, and these cutting blades are exchanged to serve cutting corresponding to the target, namely, sheath or optical fiber. Since it is possible to cut the sheath and the optical fiber under almost ideal condition that fits the used materials, the sheared edge of the sheathed optical fiber is relatively easily made flat with reliability. Further, since the durability of the cutting blades is improved, the life of the cutting blade is extended, and the interval for replacing the cutting blade with a new one is extended, the cutting apparatus becomes economically available. In addition, since the interval for replacing the cutting blade with a new one is extended, the downtime of the cutting apparatus is shortened, the working efficiency is improved, and its maintenance becomes easy.